1. Technical Field
Exemplary embodiments of the present invention relate to a phase-change random access memory (PCRAM) device and a method of manufacturing the same, and more particularly, to a PCRAM device including a diode and a method of manufacturing the same.
2. Related Art
PCRAM devices store data using a phase-change material, which is changed to a crystalline state or an amorphous state while the phase-change material is heated and cooled. That is, since the phase-change material has low resistance in the crystalline state and high resistance in the amorphous state, the crystalline state may be defined as SET or logic level “0” and the amorphous state may be defined as RESET or logic level “1”.
As the phase-change material applied to the PCRAM devices, a chalcogenide compound (Ge—Sb—Te: GST) including germanium (Ge), antimony (Sb), tellurium (Te) has been mainly used. The crystalline state in the phase-change material such as GST may be changed by heat generated according to a current intensity and applied time.
The PCRAM devices may include a plurality of phase-change memory cells formed at intersections of word lines and bit lines. The phase-change memory cell includes a resistor of which a value is changed based on a through current and an access device configured to control the current provided to the resistor.
PNP bipolar transistors MOS transistors, or PN diodes may be used as an access device and the PN diodes occupied with a narrow area are mainly used as an access device of high-integrated PCRAM devices.
When the device is driven using the PN diode, current does not flow in an off current state and a large amount of current flows in on current state even in a lower voltage so that the PN diode provide stable operations for many cells.
However, leakage current occurs often in the off current state of the PN diode. Therefore, when a vertical PN diode is applied to suppress dopant diffusion in a fabrication process of a current RN diode, an undoped layer is applied to be interposed between P-type and N-type conductive layers. The dopant, movement due to thermal diffusion continuously occurs, and thus, leakage current in the off current state is increased.
Thus, a thickness of the undoped layer interposed between the P and N type conductive layers in the vertical PN diode is increased, but there is limitation to increase the height of the vertical PN diode. Reduction in the leakage current of the vertical PN diode is emerging as a main concern.